Nonlinear rheological properties of dense colloidal dispersions close to a glass transition under steady shear

TL;DR

This paper develops a first principles theoretical framework to understand the nonlinear rheological behavior of dense colloidal suspensions near the glass transition under steady shear, linking microscopic dynamics to macroscopic flow properties.

Contribution

It introduces a mode coupling based approach starting from the Smoluchowski equation, providing a quantitative description of shear thinning and yielding in colloidal glasses.

Findings

Shear thinning results from competition between structural relaxation slowdown and fluctuation decorrelation.

Mode coupling approximations enable quantitative predictions of shear-induced particle cage breaking.

Comparison with experiments confirms the theory's ability to describe nonlinear rheology.

Abstract

The nonlinear rheological properties of dense colloidal suspensions under steady shear are discussed within a first principles approach. It starts from the Smoluchowski equation of interacting Brownian particles in a given shear flow, derives generalized Green-Kubo relations, which contain the transients dynamics formally exactly, and closes the equations using mode coupling approximations. Shear thinning of colloidal fluids and dynamical yielding of colloidal glasses arise from a competition between a slowing down of structural relaxation, because of particle interactions, and enhanced decorrelation of fluctuations, caused by the shear advection of density fluctuations. The integration through transients approach takes account of the dynamic competition, translational invariance enters the concept of wavevector advection, and the mode coupling approximation enables to quantitatively explore the shear-induced suppression of particle caging and the resulting speed-up of the structural relaxation. Extended comparisons with shear stress data in the linear response and in the nonlinear regime measured in model thermo-sensitive core-shell latices are discussed. Additionally, the single particle motion under shear observed by confocal microscopy and in computer simulations is reviewed and analysed theoretically.